1. Field of the Invention
The present invention relates to fuel supply systems and more particularly to a flow divider and ecology valve for supplying fuel to an engine manifold and withdrawing fuel therefrom upon engine shut-down.
2. Description of the Related Art
Gas turbine engine fuel delivery systems may require multiple fuel manifolds and an arrangement for apportioning fuel flow among those manifolds to segregate various types of fuel nozzles for optimal engine performance. For example, U.S. Pat. No. 5,809,771 to Wernberg discloses a fuel flow splitting valve having a single piston operable in two different regions, one for modulating flow to primary and secondary engine nozzles as a function of fuel pressure and another where flow to primary and secondary engine nozzles is determined by the fixed port geometry. Also, some engines may require an ecology function that removes a set quantity of fuel from the engine fuel manifold(s) upon cessation of engine operation. Fuel removal is required to keep fuel from vaporizing into the atmosphere and to avoid fuel coking on the engine""s fuel nozzles, a condition that hinders nozzle performance. Prior art ecology systems have used an arrangement of pistons, check valves, plumbing, reservoirs and pumps to accomplish this task. In engines requiring multiple fuel manifolds, multiple ecology valves or a multiple chambered ecology valve have been used. A two chambered valve is disclosed in the abovementioned Wernberg patent. In the Wernberg system, fuel is simultaneously withdrawn from the two manifolds and a separate chamber is required for each engine manifold to ensure complete fuel removal from those manifolds upon engine shut-down. These types of architecture result in complex high cost and weight ecology systems.
It is desirable to minimize the fuel remaining in an engine intake manifold upon cessation of engine operation and to provide a compact, economical ecology function for fuel supply systems. It is also desirable to achieve such an ecology function by employing a simple valve which is controlled solely by fuel flow to the manifold(s) involved. It is further desirable to provide both an ecology function and a fuel flow dividing function in a common simplistic valve mechanism.
The present invention provides solutions to the above considerations in the form of an ecology and flow divider valve module consisting of a flow shutoff and pressurizing valve assembly, and an ecology valve (piston reservoir) assembly, packaged on a common centerline, in a common body. In another form, the module includes a flow apportioning valve downstream of the shutoff and pressurizing valve.
The invention comprises, in one form thereof, a fuel flow dividing ecology valve for selectively conveying fuel from a fuel source to at least a secondary gas turbine engine intake manifold during engine operation and withdrawing fuel therefrom upon cessation of engine operation which includes a flow dividing portion and an ecology valve portion. The flow dividing valve portion has an inlet coupled to the fuel source and an outlet coupled to the secondary manifold, the flow dividing valve portion transitions from a fuel flow blocking condition to a condition in which fuel may flow from the source to the manifold solely in response to the fuel pressure differential between the inlet and the outlet. The ecology valve portion is controlled solely by the fuel pressure differential between the dividing valve portion inlet and outlet for withdrawing fuel from the secondary engine intake manifold when the engine is de-energized thereby purging the manifold of fuel, and returning withdrawn fuel to the manifold during subsequent engine operation.
Also in general, and in one form of the invention, a fuel flow dividing valve for selectively conveying fuel from a fuel source to at least a primary gas turbine engine intake manifold and a secondary gas turbine engine intake manifold during engine operation includes a pressure differential actuated flow dividing valve portion having a movable valve spool with a flow restricting inlet and first and second substantially unrestricted outlets. The first outlet is coupled to the inlet and is independent of valve condition for supplying fuel to the primary manifold. The second outlet is coupled to the inlet for supplying fuel to the secondary manifold only when the pressure differential across the flow restriction exceeds a threshold. An ecology valve portion is controlled solely by the fuel pressure differential between the fuel source and the flow restricting inlet for withdrawing fuel first from the secondary engine intake manifold and subsequently from the primary engine intake manifold when the engine is de-energized thereby purging both manifolds of fuel, and returns withdrawn fuel to the manifolds during subsequent engine operation.
An advantage of the present invention is that the flow splitter valve is nested axially within the ecology valve, which conserves size, weight, and complexity.
Another advantage of the present invention is that ecology valve is controlled solely by fuel flow to and the pressure differential across the flow splitter valve.